1. Field of the Invention
The present invention relates to a plasma etching method, or in particular to a plasma etching method suitable for etching a sample by supplying a processing gas from an electrode portion for generating a plasma or a shower plate arranged on the electrode portion in opposed relation to a sample, and transforming the processing gas into a plasma.
2. Description of the Related Art
[Prior Art 1]
A conventional plasma etching apparatus is described in EP210605B1 (JP-B-7-40567) which discloses an etching apparatus of single-wafer parallel flat plate type configured as follows.
A wafer is held in a holder. The wafer is in opposed relation to an electrode with a space not more than 2 cm. The electrode is preferably formed of single crystal silicon having a multiplicity of holes. The processing gas is supplied into a processing chamber through the holes (0.5 mm in diameter) formed in the electrode. The opposed electrode is connected separately to another terminal of the power source. Upon application of a RF voltage between the holder and the electrode, a plasma is generated in the low-pressure gas between them thereby to start the etching process. The electrode is subjected to a shock by ions to substantially the same degree as the wafer. This electrode is much thicker than a standard silicon wafer. The thickness of the electrode is preferably at least 1.8 mm.
This apparatus is used for plasma etching of an oxide. The RF voltage of 230 W is applied to the wafer and the electrode. An oxide is etched using a mixture gas containing fluorine such as a mixture of CHF3 and a small amount of O2. The total pressure of the processing gas is set to 700 mTorr.
The use of the electrode of single crystal silicon having a multiplicity of holes for supplying the processing gas greatly reduces the number of particulates generated, lengthens the service life with an improved durability, and achieves a high etching rate and a very high uniformity.
[Prior Art 2]
Another conventional plasma etching apparatus is described, for example, in Japanese Patent No. 3,066,007. This publication discloses an apparatus in which the gas introduced into a vacuum chamber is transformed into a plasma by the interaction between the electromagnet and the electromagnetic wave introduced into a flat plate by a coaxial cable thereby to process the sample. This apparatus has the following configuration.
A flat plate is arranged in opposed relation to a sample to be processed. The interval between the flat plate and the sample is set to 30 mm or not more than one half of the diameter of the sample. The flat plate is impressed, through a filter, with two frequencies, one from a power source of 300 MHz to 500 MHz inclusive (450 MHz in the case under consideration) for producing a plasma, and the other from a power source of 500 kHz to 30 MHz inclusive (13.56 MHz in the case under consideration). The surface of the flat plate is formed of silicon, and a processing gas is introduced into the vacuum chamber from a plurality of the holes formed in the silicon surface. The electromagnetic wave of the 13.56 MHz power source has the function of adjusting the potential formed between the silicon surface and the plasma. The sample is supplied with an electromagnetic wave of 800 kHz power for controlling the ion energy entering the sample from the plasma.
A silicon oxide film is etched by this apparatus using a mixture gas of argon gas and C4F8 as a processing gas. The pressure of the processing gas is 2 Pa. The flat plate is supplied with 800 W power from a 450 MHz power source thereby to produce a plasma. The flat plate is also impressed with the power of 300 W from a 13.56 MHz power source in superposition on the power of 450 MHz.
In this apparatus, the active species in the plasma can be controlled independently of the plasma production. Especially, the effect of controlling the active species can be remarkably increased and a highly accurate plasma process can be realized by controlling the interval between the sample and the flat plate, the material on the flat plate and the electromagnetic wave applied in superposition to the flat plate.
[Prior Art 3]
Still another conventional plasma processing apparatus is described in JP-A-11-3799. This publication discloses a plasma processing apparatus comprising a processing chamber including a plasma production unit on a base chamber, an antenna connected with a high-frequency power source, a substrate stage arranged in the processing chamber, a biasing power supply connected to the substrate stage, and a inclined shower plate for controlling the flow of the processing gas supplied into the processing chamber. This publication contains the description to the effect that any of an induction coupled plasma source, a capacitance coupled plasma source and a microwave plasma source is applicable for plasma production.
The inclined shower plate includes a plate of a metal or a dielectric material formed with a multiplicity of holes of small diameter (about φ0.5 to 3 mm) obliquely along the circumferences of circles concentric about the center axis of the plate. As a result, the flow velocity of the processing gas passing through the plasma area has a component in the circumferential direction, and the uniformity, along the circumference, of the active species transported onto the processed substrate is improved.